Intentionally Forgetting For A Spotless Mind

A new brain scanning study shows that people can intentionally forget past experiences by changing how they think about the context of those memories.

The findings have a range of potential applications centered on enhancing desired memories, such as developing new educational tools, or diminishing harmful memories, including treatments for post-traumatic stress disorder, according to researchers from Dartmouth College and Princeton University.

Since ancient times, memory theorists have known that we use context — the situation we’re in, including sights, sounds, smells, where we are, who we are with — to organize and retrieve our memories.

But the researchers for this study wanted to know whether and how people can intentionally forget past experiences.

They also used a new twist on a centuries-old psychological research technique of having subjects memorize and recall a list of unrelated words.

In the new study, researchers showed participants images of outdoor scenes, such as forests, mountains, and beaches, as they studied two lists of random words. Researchers then told the participants to either forget or remember the first list prior to studying the second list.

“Our hope was the scene images would bias the background, or contextual, thoughts that people had as they studied the words to include scene-related thoughts,” explained lead author Dr. Jeremy Manning, an assistant professor of psychological and brain sciences at Dartmouth.

“We used fMRI to track how much people were thinking of scene-related things at each moment during our experiment. That allowed us to track, on a moment-by-moment basis, how those scene or context representations faded in and out of people’s thoughts over time.”

Right after the study’s participants were told to forget the random words presented to them interspersed between scene images, the fMRI showed that they “flushed out” the scene-related activity from their brains, according to the researchers.

“It’s like intentionally pushing thoughts of your grandmother’s cooking out of your mind if you don’t want to think about your grandmother at that moment,” Manning said. “We were able to physically measure and quantify that process using brain data.”

When the researchers told participants to remember the list rather than forget it, this flushing out of scene-related thoughts didn’t occur.

Additionally, the amount that people flushed out scene-related thoughts predicted how many of the studied words they would later remember, which shows the process is effective at facilitating forgetting, the researchers said.

The study has two important implications, according to the scientists.

“First, memory studies are often concerned with how we remember rather than how we forget, and forgetting is typically viewed as a ‘failure’ in some sense, but sometimes forgetting can be beneficial, too,” Manning said.

“For example, we might want to forget a traumatic event, such as soldiers with PTSD. Or we might want to get old information ‘out of our head,’ so we can focus on learning new material. Our study identified one mechanism that supports these processes.”

The second implication is more subtle, but also important, he said.

“It’s very difficult to specifically identify the neural representations of contextual information,” he said. “If you consider the context you experience something in, we’re really referring to the enormously complex, seemingly random thoughts you had during that experience. Those thoughts are presumably idiosyncratic to you as an individual, and they’re also potentially unique to that specific moment.

“So, tracking the neural representations of these things is extremely challenging because we only ever have one measurement of a particular context. Therefore, you can’t directly train a computer to recognize what context ‘looks like’ in the brain because context is a continually moving and evolving target.

“In our study, we sidestepped this issue using a novel experimental manipulation — we biased people to incorporate those scene images into the thoughts they had when they studied new words,” he said. “Since those scenes were common across people and over time, we were able to use fMRI to track the associated mental representations from moment to moment.”

The study was published in the journal Psychonomic Bulletin and Review.

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About Janice Wood

Janice Wood is a long-time writer and editor who began working at a daily newspaper before graduating from college. She has worked at a variety of newspapers, magazines and websites, covering everything from aviation to finance to healthcare.